Highly stretchable electric circuits from a composite material of silver nanoparticles and elastomeric fibres.

Conductive electrodes and electric circuits that can remain active and electrically stable under large mechanical deformations are highly desirable for applications such as flexible displays, field-effect transistors, energy-related devices, smart clothing and actuators. However, high conductivity and stretchability seem to be mutually exclusive parameters. The most promising solution to this problem has been to use one-dimensional nanostructures such as carbon nanotubes and metal nanowires coated on a stretchable fabric, metal stripes with a wavy geometry, composite elastomers embedding conductive fillers and interpenetrating networks of a liquid metal and rubber. At present, the conductivity values at large strains remain too low to satisfy requirements for practical applications. Moreover, the ability to make arbitrary patterns over large areas is also desirable. Here, we introduce a conductive composite mat of silver nanoparticles and rubber fibres that allows the formation of highly stretchable circuits through a fabrication process that is compatible with any substrate and scalable for large-area applications. A silver nanoparticle precursor is absorbed in electrospun poly (styrene-block-butadiene-block-styrene) (SBS) rubber fibres and then converted into silver nanoparticles directly in the fibre mat. Percolation of the silver nanoparticles inside the fibres leads to a high bulk conductivity, which is preserved at large deformations (σ ≈ 2,200 S cm(-1) at 100% strain for a 150-µm-thick mat). We design electric circuits directly on the electrospun fibre mat by nozzle printing, inkjet printing and spray printing of the precursor solution and fabricate a highly stretchable antenna, a strain sensor and a highly stretchable light-emitting diode as examples of applications.

Ordering evolution of block copolymer thin films upon solvent-annealing process.

Morphologies of polystyrene-block-poly(2-vinylpyridine) copolymer (S2VP) thin films, which are forming poly(2-vinylpyridine) cylinders in bulk phase, were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM) to account for their ordering behavior induced by solvent annealing. Initially, when the copolymer was dissolved in toluene, which is selective solvent for majority polystyrene (PS) blocks, and was spin-coated on Si substrates, dimple-type micellar structures of S2VP were formed. After the film was placed in a solvent-annealing chamber covered with a lid under the existence of chloroform, surface morphologies of S2VP were measured as a function of annealing time. In this study, it was found that the morphologies of S2VP thin film repeated the cycle of the creation and extinction of various morphologies on ordering process. Namely, S2VP exhibited the various transformations between different morphologies, including highly disordered state, cylinders normal to the plane, and cylinders parallel to the plane. Each of the morphologies observed here was employed as a template to synthesize gold (Au) nanoparticles or nanowires. The arrays of Au nano-objects were used to tune a surface plasmon resonance.

High-performance organic optoelectronic devices enhanced by surface plasmon resonance.

The surface plasmon effect on polymer solar cells and polymer light-emitting diodes is demonstrated by using metal nanoparticles prepared from block copolymer templates. Light absorption of the polymer thin layer is increased with the incorporation of metallic nanostructures, resulting in a significant surface plasmon effect in the optoelectronic devices.

Development of various PS-b-P4VP micellar morphologies: fabrication of inorganic nanostructures from micellar templates.

We demonstrate a simple route for preparing various micellar nanostructures, like spheres, cylinders, and vesicles, by spin-coating or drop-casting process of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymer solutions in pure tetrahydrofuran (THF), THF/water, and THF/ethanol mixture. Upon drying, a solvent selectivity plays an important role in determining micellar nanostructures in thin films. In solution, micellar sizes and shapes of these PS-b-P4VP copolymers were investigated by dynamic and static light scattering. Immediately after spin-coating the polymer solutions, surface and internal morphologies of the films were observed by atomic force microscopy and transmission electron microscopy. As the polymer concentration in THF or the amounts of water or ethanol added in THF solutions was varied, a remarkable difference in the PS-b-P4VP micellar morphologies was observed, from which spherical or cylindrical or vesicular micelles were developed. These micellar films were used as scaffolds or templates for fabricating metal nanodots or nanowires arrays.

Supramolecular assembly of end-functionalized polymer mixtures confined in nanospheres.

Supramolecular assembly of functionalized polymers, capable of forming block copolymer-like molecular clusters, has emerged as a promising alternative for creating nanoscopically ordered structures. Here, we demonstrate that nanospheres, which have intriguing internal nanodomains and controllable surface functionality, can be fabricated by supramolecular assembly of two complementarily end-interacting species of mono-end-functionalized polymers using the self-organized precipitation (SORP) method. An exotic internal morphology, hierarchically organized structure of perforated spherical layers, was formed inside the nanosphere prepared from the stoichiometric mixture of the end-functionalized polymers, which is due to the formation of diblock-like supramolecules and their packing frustration in the spherically confined nanospace. When the mixing ratio of the two end-functionalized polymers differs from the stoichiometric ratio, the nanoparticle surface is enriched with an excess of unpaired functionalized groups, which therefore provides us with a useful way to precisely control the surface functionality of the nanoparticles.

Enhanced open circuit voltage by hydrophilic ionic liquids as buffer layer in conjugated polymer-nanoporous titania hybrid solar cells.

We demonstrate the fabrication of a nanoporous titania (NP-TiO(2)) network structure by using a polystylene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer template and modifying the surface of NP-TiO(2) with ionic liquids (ILs), bmim-BF(4) and benmim-Cl. The effect of the molecular weight of PS-b-P4VP on the morphology of the NP-TiO(2) and IL-modified NP-TiO(2) are characterized by scanning electron microscopy and contact angle measurements. Subsequently, hybrid solar cells are fabricated using MEH-PPV and NP-TiO(2), and the effect of IL layers and IL concentrations on device performances are evaluated under AM 1.5 G illumination. The devices containing bmim-BF(4) and benmim-Cl show drastically enhanced open circuit voltages (V(oc)) of 1.05 V and 0.91 V, respectively, while the reference device without an IL layer exhibits a V(oc) of 0.60 V. Significantly improved V(oc) can be attributed to the change in interfacial energy levels by formation of ionic double layers at the TiO(2)/IL and at the IL/MEH-PPV interfaces. We also observed the trend that short circuit current decreased and V(oc) increased with increasing IL concentration, which is ascribed to interruption of charge transfer from MEH-PPV to TiO(2) and the change in interfacial energy level by shifting the vacuum level, respectively.

Fabrication of disposable topographic silicon oxide from sawtoothed patterns: control of arrays of gold nanoparticles.

Disposable topographic silicon oxide patterns were fabricated from polymeric replicas of sawtoothed glass surfaces, spin-coating of poly(dimethylsiloxane) (PDMS) thin films, and thermal annealing at certain temperature and followed by oxygen plasma treatment of the thin PDMS layer. A simple imprinting process was used to fabricate the replicated PDMS and PS patterns from sawtoothed glass surfaces. Next, thin layers of PDMS films having different thicknesses were spin-coated onto the sawtoothed PS surfaces and annealed at 60 degrees C to be drawn the PDMS into the valley of the sawtoothed PS surfaces, followed by oxygen plasma treatment to fabricate topographic silicon oxide patterns. By control of the thickness of PDMS layers, silicon oxide patterns having various line widths were fabricated. The silicon oxide topographic patterns were used to direct the self-assembly of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer thin films via solvent annealing process. A highly ordered PS-b-P2VP micellar structure was used to let gold precursor complex with P2VP chains, and followed by oxygen plasma treatment. When the PS-b-P2VP thin films containing gold salts were exposed to oxygen plasma environments, gold salts were reduced to pure gold nanoparticles without changing high degree of lateral order, while polymers were completely degraded. As the width of trough and crest in topographic patterns increases, the number of gold arrays and size of gold nanoparticles are tuned. In the final step, the silicon oxide topographic patterns were selectively removed by wet etching process without changing the arrays of gold nanoparticles.

Fast size-exclusion chromatography at high temperature.

We report on the size-exclusion chromatography (SEC) operated at high column temperature to reduce the analysis time. The column temperature was raised beyond the normal boiling point of the eluent and a sufficient column backpressure was applied to prevent the mobile phase from boiling by inserting a narrow bore tubing between the separation column and the detector. The narrow bore tubing also functions to cool the effluent down to the room temperature before it reaches the detector. Therefore, normal SEC detectors can be used without any modification. It was confirmed that the SEC analysis time could be shortened significantly by the high-temperature operation without serious deterioration in the resolution.

[Estimating the burden of psychiatric disorder in Korea].

OBJECTIVES: This study estimated the burden of disease especially caused by psychiatric disorders in Korea by using DALY, a composite indicator that was recently developed by the Global Burden of Disease study group. METHODS: First, 11 of the major psychiatric disorders in Korea were selected based on the ICD-10. Second, the burden of disease due to premature death was estimated by using YLLs (years of life lost due to premature death). Third, for the calculation of the YLD (years lived with disability), the following parameters were estimated in the formula: the incidence rate, the prevalence rate and the disability weight of each psychiatric disorder. Last, we estimated the DALY of the psychiatric disorders by adding the YLLs and YLDs. RESULTS: The burden of psychiatric disorder per 100,000 people was attributed mainly to unipolar major depression (1,278 person-years), schizophrenia (638 person-years) and alcohol use disorder (287 person-years). For males, schizophrenia (596 person-years) and alcohol use disorder (491 person-years) caused the highest burden. For females, unipolar major depression (1,749 person-years) and schizophrenia (680 person-years) cause the highest burden. As analyzed by gender and age group, alcohol use disorder causes a higher burden than schizophrenia in men aged 40 years and older. For females, unipolar major depression causes the highest burden in all age groups. CONCLUSIONS: We found that each of the psychiatric disorders that cause the highest burden is different according to gender and age group. This study's results can provide a rational basis to plan a national health policy regarding the burden of disease caused by psychiatric disorders.